From Pillar to Post: More Automotive Definitions - Ate Up With Motor From Pillar to Post: More Automotive Definitions Periodically, we feel it’s worth taking the time to define some of the terms we throw around with which some readers may not be familiar. This week, we examine some of the terminology of automotive design. First, let’s review some basics: Axle: This is a term that has several related but distinct meanings. An axle is any set of two or more of a vehicle’s wheels that rotate around a common axis; the beam or assembly connecting those wheels is also called an axle. Of course, many modern vehicles have independent suspension, with no direct physical connection between the wheels. In such vehicles, the term axle is still applied in a more abstract sense to mean the imaginary line between the centers of the left and right wheels. Wheelbase: The horizontal distance between the respective wheel centers of the front and rear axles. On passenger cars, that distance is usually — but not always — the same from right to left. The wheelbase quoted in a car’s specifications is measured with the car stationary and unladen; depending on the suspension geometry, the actual wheelbase may change as each wheel moves through its range of travel.

A car’s wheelbase is a critical dimension in many respects, affecting ride quality, maneuverability, and passenger space. In general, a longer wheelbase benefits ride quality (because it lowers the frequency of ride motions) and passenger room (by allowing more legroom), but reduces maneuverability by spreading the car’s mass over a longer distance, thus raising its polar moment of inertia. Conversely, a short wheelbase provides better maneuverability at the cost of a choppier ride and less useful interior room. Overhang: Front overhang is the distance between the front axle and the front end of the car; rear overhang is the distance between the rear axle and the rear end of the car. Overall length: The distance from the front of the vehicle to the rear, including bumpers. A vehicle’s overall length is equal to the sum of the wheelbase, the front overhang, and the rear overhang. In the illustration above, A is the front overhang; B is the wheelbase; and C is the rear overhang. Naturally, overall length = A + B + C.

Track or Tread Width: A vehicle’s tread width (or track) is the distance between the horizontal centers of the left and right wheels on each axle. The track widths of the front and rear axles are often slightly different, so a car’s specifications will usually list front and rear track separately. (The terms “track” and “tread width” are often used interchangeably, but “track” has become more common to avoid confusion with the width of each tire.) As with the wheelbase, the track widths shown in a car’s specifications are static measurements; depending on the suspension layout, track may change as the car’s wheels move through their suspension travel. Couple: Couple can mean a variety of different things in automotive engineering, but to designers, couple distance is the distance between the driver’s hip joint when seated (which designers call the “H-point”) and the rear axle line. A close-coupled car is one in which this distance is very short. The modern BMW Z4 roadster, which has the cabin pushed so far back that the driver is practically sitting on the rear axle, is a close-coupled design.

Next, let’s define a couple of terms the describe how components are positioned inside the vehicle.Transverse or Longitudinal: Naturally enough, transverse means sideways, while longitudinal means lengthwise. In a car, if the component is parallel to the axles when seen in plan view (that is, when viewed from overhead), it is transverse. If it is perpendicular to the axles, it is longitudinal. With automotive engines, a transverse engine is mounted so that its crankshaft is parallel to the axles while a longitudinal engine (also called a north-south engine) is mounted so that its crankshaft is perpendicular to the axle. Leading or Trailing: The edge of a component nearest the front of the vehicle is called the leading edge; the edge furthest from the front of the vehicle is the trailing edge. This can be a little confusing when applied to suspension components because they’re described in terms of their relationship to the body rather than the wheel. A suspension link that connects to the wheel behind the point where it connects to the body is called a trailing link (or trailing arm). A suspension arm that connects to the wheel ahead of the point where it connects to the body is called a leading link.

Next, let’s look at some terms related to the body. Body panels: The outer skin of most cars is usually separate from the inner body structure and consists of panels of metal or plastic bolted, welded, or glued to the inner structure. (It’s worth noting here that while each exterior panel may appear to be a single piece, it is typically an amalgamation of several smaller pieces that are welded or otherwise bonded together.) Since the body panels of most modern cars are sheet steel, a car’s skin is often generically called sheet metal, although some cars use plastic or carbon fiber for certain exterior panels, either to save weight or better resist parking lot dings. The spaces between body panels are called panel gaps or shutlines. Hood: Since we are American, we describe the panel that covers a car’s engine compartment as the hood; English-speaking readers elsewhere in the world call this the bonnet. (Since “hood” in British usage refers to a convertible top, we sometimes elect to use the word “bonnet” to avoid confusing our non-U.S. readers.) Deck: When we’re talking about a car’s body, the deck is the section of the body behind the rear window.

On front-engined vehicles, the deck (if there is one) usually contains the cargo area, which our American readers describe as the trunk and British readers call the boot. If the deck incorporates an opening panel, that panel is known as a decklid. (The word “deck” also refers to the upper surface of the engine block, where the cylinder head mates to the block. Customizers also use “deck” as a verb, referring to the removal of all exterior trim from the deck and decklid.) On some cars, there is a gap between the base of the rear window and the leading edge of the decklid; for obscure reasons, some stylists call this area the “Dutchman.” Continental kit: A spare wheel mounted externally on a car’s deck or rear bumper, often with a cover painted the color of the body and embellished with chrome. Buick did not offer a Continental kit as a factory option in the fifties, but various dealers and aftermarket companies offered accessory kits to add one. In the twenties and thirties, some designers — and some buyers — were keen on side mounts: spare wheels mounted in the front fenders, behind the front wheels.

Like the later Continental kits, side mount spares frequently had body-colored covers for a more streamlined look. By the late thirties, they were considered increasingly archaic and they fell out of favor just before World War II. This 1936 Cadillac V-12 convertible shows off its neatly trimmed and decorated side mount spare wheel. Like many side mounts of this era, the mirror is clipped to the top of the wheel’s cover. A major drawback of side mounts was that moisture would pool in the well under the wheel, promoting corrosion. Wheel well or wheelhouse: The area in each corner of the car’s body that contains the wheel — and the clearance needed for it to turn and move up and down through its suspension travel. Fender: The exterior body panel surrounding each wheel well. (Our British readers call this a wing; American designers sometimes refer to the rear fenders as quarter panels.) The original purpose of fenders was to keep the wheels from throwing mud, water, or dirt onto the windshield and interior. A fender skirt is a trim panel that covers part of the wheel opening. Many fender skirts are removable to facilitate tire changes or other maintenance.

In the thirties and forties, automotive fenders became progressively more streamlined and integrated into the body. By the late fifties, they had almost completely “melted” into the surrounding body. Fender skirts, however, have never quite caught on, perhaps because they complicate tire-changing. Cowl: The portion of the body structure below the base of the windshield to which the front fenders are attached. In a front-engine car, the cowl incorporates the firewall, the panel that separates the engine compartment from the cabin. The cowl usually contains the car’s heating and ventilation system (which on modern cars generally draw their air from a plenum at the base of the windshield). The cowl is a major structural element and is typically the second-largest (and most complex) single piece of the body. Manufacturers will often share the same cowl structure between several vehicles. For example, the 1961–1966 Ford Thunderbird shared its cowl with the contemporary Lincoln Continental. Floorpan: The bottom of a vehicle’s body, generally beginning at the cowl and comprising the floor of the cabin and cargo area. On many mass-production cars, the floorpan is one big, complex steel stamping.

Since this is usually the largest and most expensive single piece of the body, it’s common for manufacturers to use the same floorpan (or variations of it that can be made with the same machinery) for several different models. Until the early fifties, many cars had pop-up vents in the cowl, at the base of the windshield. Modern cars still take their ventilation air from this area, although usually through a grille just behind and below the trailing edge of the hood, in the same area as the windshield wipers. Sill: Sometimes called the rocker area, the sill is the outermost longitudinal section of each body side, running beneath the door openings from the trailing edge of the front wheelhouse to the leading edge of the rear wheel opening. The sills are important structural members, particularly in unitized or semi-unitized vehicles, and typically provide a great deal of the body’s total bending stiffness. Early unitized cars, particularly ones intended to offered in convertible form, often had large, complex sill structures. Rocker panel: The outside of the rocker area, which may be either a separate body panel concealing the sill (and/or the frame rail beneath it) or simply the exposed, finished outer section of the sill itself.

Some cars cover the rocker panel with a plastic or chrome rocker molding, either for decoration or to protect the rocker panel from stone chips and road salt. Rub strip: A horizontal trim strip or molding running across the door and sometimes the inside of the front fender to protect against dings and scratches from the doors of other cars. In recent years, it has become popular to omit the rub strips for a cleaner appearance, although the absence of protective trim tends to result in an assortment of minor dings and scratches after a few years in the real world. Roof pillars: The vertical pillars (or posts; the terms are used interchangeably) that support a car’s roof. The forward pillars, which also support the windshield, are called A-pillars. Center pillars located behind the driver’s seat but ahead of the rear seats (if any) are called B-pillars. The rear pillars, behind the cabin, are called C-pillars. If the car has an additional set of pillars behind the C-pillars, such as the rearmost pillars of a station wagon (estate car), they are called D-pillars.

(“Post” may be used interchangeably with “pillar” in this sense.) In the fifties and sixties, there was a great craze for pillarless hardtops, which had no B-posts. Some manufacturers offered hardtop coupes, sedans, and even station wagons. Even if a vehicle has no B-pillars, the pillars behind the cabin are still called C-pillars and D-pillars respectively. Although true pillarless hardtops are rare today, many cars still strive for a hardtop look by concealing the B-post behind a darkened section of the rear quarter window. This early-nineties Dodge Stealth shows off a typical “blackout pillar” treatment. Note that the front windows have no frames, adding to the effect. Sail panel: The body panel covering the rearmost roof pillar. In the sixties and seventies, there was a brief vogue for “flying buttress” roof designs, in which the sail panels extended further back than the roof pillars themselves. This is still occasionally seen on mid-engine cars, although it has fallen out of favor for most ordinary passenger cars. Rake: Stylists use the term rake (or fast) to describe the angle of the windshield.

In the forties and fifties, customizers and hot-rodders also coined the word rake (sometimes California rake) to describe a vehicle whose tail is noticeably higher than its nose. Greenhouse: The collective term for the roof, roof pillars, side windows, windshield, and backlight. Beltline: The uppermost horizontal edge of the doors and body sides, below the greenhouse. Tumblehome: In automotive terms, the angle of the sides of the greenhouse (when viewed from the front or rear) relative to the vertical plane. If the side windows are completely vertical, tumblehome is zero. Beginning around the late 1950s, American stylists became enamored of increasingly radical tumblehome as a way to make a vehicle look lower than it was. However, extreme tumblehome generally requires the use of curved glass for the side windows (which is more expensive than flat glass) and can cut significantly into passengers’ head and shoulder room. Chrysler’s early-seventies “fuselage styling” theme emphasized some of the industry’s most extreme tumblehome. The sides curve inward so sharply that the top edge of the side window sits practically above the driver’s shoulder.

Light: Stylists sometimes refer to a car’s windows as “lights.” For example, small windows between the roof pillars and the car’s side windows are sometimes called quarterlights (or quarter windows). The rear window is called the backlight. A car with three windows on each side (for example, two regular windows and a quarter window) is called a “six-light” design, while one with only two windows per side is called a “four-light” design. A 1967 Pontiac Firebird shows off its front quarterlight (which GM originally called “Venti-Planes”). Note also the prominent chrome reveals around the side window and windshield. Reveal: An exterior molding or decorative trim piece surrounding a window or other exterior body component. Drip rail: A molding U-shaped channel at the outer edges of the roof, above the doors, that channels rain water away from the side windows. Modesty panel: A body panel below the front or rear bumper that hides the ends of the frame or body structure. Airdam: A modesty panel under a car’s front bumper that controls the flow of air under the car.

The main purpose of the airdam is to force air to flow around the car rather than under it in the interests of reducing aerodynamic drag and lift. On many modern cars, the airdam also channels air into the radiator, the engine’s air intake, and sometimes the front brakes. Most modern cars have airdams, but few are as aggressive as that of the Mitsubishi Lancer Evo. The extended lip also functions as a spoiler. Spoiler: A device that improves a car’s aerodynamics by “spoiling” aerodynamic drag, lift, or both. Small lip spoilers are commonly incorporated into the airdam and mounted on (or molded into) the rear decklid. Although spoilers and wings are more often cosmetic than aerodynamically useful, lip spoilers are often functional. (We’ve noted that the tinier and more anemic a spoiler looks, the more likely it is to actually work, although this tongue-in-cheek “rule” obviously ignores the more complex aerodynamics involved.) Scoop: An opening that allows outside air to pass through a body panel. A functional scoop may serve to channel air into the cabin’s ventilation system; the engine’s intake manifold, radiator, or intercooler; or the brakes.

Some scoops have more than one plenum, allowing them to perform several of these functions at once, but it’s more common for a scoop to be strictly decorative. Mid-engine cars, like this Lotus Elise, typically have a formidable array of functional scoops to channel cooling and intake air into the engine. Louver: A slot or vent that either admits or exhausts air. Working louvers may provide additional airflow to intercoolers or brakes or allow hot air to leave the cabin or engine compartment. Nonfunctional fender louvers periodically become popular as cosmetic add-ons. The Ford GT shows off its array of engine cooling louvers. The GT has a great deal of heat to dissipate; under the cover is a 5,409 cc (330 cu. in.) DOHC V-8 with a Lysholm-type supercharger, making 550 horsepower (410 kW). Belly pan: A smooth pan or tray mounted on the underside of the car. Since underbody components like the engine oil pan, frame rails, and exhaust pipes tend to be aerodynamically cluttered, the typical purpose of the belly pan is to reduce drag.

(Many modern cars have a detachable plastic cover under the engine, which serves a similar purpose at less cost than a full pan.) On some modern exotic sports cars, the belly pan incorporates venturi to control the speed of air passing under the car, which can be used to provide negative lift (downforce). The slots under the rear bumper of this Ferrari F430 are diffusers for the underbody venturi. Although the F430 has no wings and only a modest lip spoiler under the nose, the underbody channels enable it to produce more than 600 lbs (2,670 N) of downforce at 185 mph (300 km/h). # # # NOTE The typeface used in the image labels is Liberation Sans, one of the Liberation Fonts, which are © 2012 Red Hat, Inc., used here under the SIL Open Font License, Version 1.1 . LIBERATION is a trademark of Red Hat, Inc.

Axle alignment critical to set wheels and tires in optimum position; TMC manual and educated technicians can help Market Stats Advertisement Home > Distributors, Upfitters > Axle alignment critical to set wheels and tires in optimum position; TMC manual and educated technicians can help Axle alignment critical to set wheels and tires in optimum position; TMC manual and educated technicians can help Mar 1, 2013 Rick Weber | Trailer/Body Builders Comments 0 Advertisement AXLE alignment is necessary to set the wheels and tires in the optimum position for maximum tire performance, according to Rick Martin, Meritor LLC's training manager for North America. “Axles are aligned in a static position so that when the vehicle is operating dynamically, the wheels and tires are in an optimum position with the road surface,” he said. “That optimum position is whatever it takes to get best tire life and best traction.” He said toe-in is when wheels are closer together in the front than in the back, while toe-out is when the wheels are closer together in the back than in the front. Toe is necessary to compensate for steering-component deflection.

“We set the toe at 1/16" because when you're going down the highway with the wheels toe-in, the road friction between the rubber and road is going to pull the tires out in a straight direction, which is steering deflection,” he said. Steer-axle toe is adjustable to reduce wear to the leading edge of the tire and also to avoid road wander. Excessive toe-in wears the outside edge of tires, while excessive toe-out wears the inside edge of the tires. “If have excessive toe in either direction, there's scrubbing of tires,” he said. “And as you lay a hand across the tire, you feel a knife edge going in one direction and smooth in the other direction. Toe is adjusted in a static condition so that the tires will run in a straight line under a dynamic condition.” He said there are all kinds of specifications differences out there, so the Technology & Maintenance Council (TMC) has produced a manual of recommended practices on alignment, with a target value of 1/16" toe-in. “Most tire wear is caused by incorrect toe settings,” Martin said. “The second-highest issue is axle-camber alignment. Toe adjustment is the responsibility of the vehicle manufacturer.

The reason why is when we build axles in the parallelogram format, it has a beam across two steering arms. We set the toe at the plant.” Martin said camber is the angle of the tire in relation to the ground. The goal is a positive camber, which occurs when the distance between the top of wheels is greater than the distance between the bottom of the wheels at ground level. “A small amount of positive camber is built into the axle beam and knuckle by the axle manufacturer,” he said. “It's manufactured at positive ¼ degree. When it gets into a truck, it can be a positive or negative. When you think of a negative, you think that's going to be tire-wear issue. But a two-year study shows that camber is not one of biggest tire-wearing issues. Your toe and axle alignment are what you need to be looking at. “TMC's target value is less than ¼ degree either side. You want to shoot for that. The camber angle is not adjustable. It is machined into both the axle beam and the knuckle. If you find that an axle beam is out of camber specs, you need to get us involved.

In my 20 years with this company I've replaced three axle beams. Bending of axle beams is not recommended by axle manufacturers and will void the axle warranty.” Martin said caster is the tilt of the kingpin center line when viewed from the side of the vehicle. The caster angle is the angle from the vertical position to the center line of the kingpin. If the top of the kingpin axis is toward the rear of the vehicle, the caster is positive. A slight positive caster creates a self-aligning action that helps to stabilize the vehicle after turning and for driving straight ahead. Too much caster will increase steering effort or may amplify a shimmy condition. He said the TMC target value is left +3½ degrees and right +4 degrees. “They're talking about when you bring the vehicle in and do an alignment,” he said. “You try to set that alignment to that specific target value the best you can. We all agreed upon that and hopefully the industry can run with that. Caster is the responsibility of the vehicle manufacturer.” When turning, the inner wheel must turn at a greater angle than the outer wheel, he said. It rotates in a smaller circle.

“At only one point in time during that turn do both tires really make a free-rolling state,” he said. “Every other time, they're scuffing. “This angle is the turning radius angle, often called the Ackerman Angle. The angle is built into the design of the tie rod arms to give the best possible road contact and to minimize tire wear during turns. If the angle is not within specifications, premature tire wear will occur. The Ackerman angle is not adjustable. Hard parts must be replaced to set the proper angle for a particular OEM and wheelbase.” Axle not perpendicular He said that with tandem axle misalignment, you have skew and thrust. That means the axle is not perpendicular to the frame. “When that axle not in there straight and parallel to the front steer axle, then you will have a push situation,” he said. “Then the driver has to compensate. When you have a tandem axle out of alignment and the driver has to turn the wheel in the other direction to compensate, you can actually get tire wear on the front steer tires that looks exactly like camber wear. You have to do a full vehicle alignment to see where the problem really lies.

Most of the time, it's going to be tandem axle alignment.” Scrub angle is formed by two thrust lines of a tandem axle vehicle (parallelism). The thrust angle is an angle formed by the centerline of the vehicle frame and the direction that an axle points (square). Irregular tire wear will appear on all wheel ends with tandems out of alignment, he said. The TMC target value for scrub (parallelism) and thrust (square) is zero degrees. “Both of them need to be perpendicular to the axle and parallel to one another,” he said. “And that's called a zero.” Martin said it's not different on a trailer: Trailer alignment has to meet alignment specifications. “When we build an axle housing for a drive axle, we do camber it and we do toe it,” he said. “That's the big axle housing under fifth wheel. There are no specifications in the field for checking that. We have engineering specifications. “Trailer axle alignment is a function of three parameters: axle orientation, which is adjustable; axle camber, which is non-adjustable; and axle toe, which is non-adjustable. Our axle will come camber or non-camber, depending on the customer. It depends on where you're running.

We've lost a lot of roads that had heavy crowns, and we have interstate highway systems, so even on a front-steer axle, we don't buy a front-steer axle camber any more. When it comes out of a facility's manufacturing plant, it's ¼-degree positive on both ends. We used to have bias for road crown.” Martin said axle orientation is defined as the positioning of the axle assembly relative to the vehicle on which it is installed. On a single-axle vehicle, the axle is positioned relative to the vehicle. On a multiple-axle vehicle, the front axle is positioned relative to the vehicle, then the remaining axles are positioned so they are parallel to this axle. “There are all different methods of doing this,” he said, “and they're all proven.” Forward-axle dimensions are measured from the kingpin to the axle centerline. If the measurement between “A” and “B” is greater than 1/8", the forward axle must be adjusted. If the measurement between “A” and “B” is less than 1/8", the forward axle does not require adjustment. Rear-axle dimensions are measured from the forward axle centerline to the rear axle centerline.

If the measurement between “C” and “D” is greater than 1/16", the rear axle must be adjusted. If the measurement between “C” and “D” is less than 1/16", the rear axle does not require adjustment. “You can't over-preload a wheel bearing or it will burn up in a quick time frame, so you have to have wheel bearing end play if you're doing a commissioned wheel bearing adjustment,” he said. “Maximum tapered roller bearing life is achieved at 0.001" preload. What's maximum life for you? You won't lose wheel seals. You won't get brake alignments coated with grease.” A pre-alignment maintenance inspection check for condition and wear includes: cold tire pressure; Pitman arm for proper torque on steering box; draglink for wear; steering arm in the knuckle to make sure it's working properly; tie-rod ends. “There are all kinds of ways to check them,” he said. “You can take four-, six-, eight-foot bar and jam it against the I-beam and push up on the cross tube and always get movement out of tie-rod assembles.

That's because you're using enough pressure to compress the spring inside the ball joint. “I've spent 43 years in this industry. I've been in both automotive and heavy truck, everywhere from mechanic to where I am now. Doctors practice every day, mechanics practice every day and learn every day. There's no way every one of us can answer all questions about everything technical. That's why there's supporting literature. That's why there are TMC Guidelines for Total Vehicle Alignment, with 45 pages of excellent information. It also has forms for doing tire checks and suspension tire wear recordkeeping.” (To receive a manual, call 1-866-821-3468 or go to .) Martin listed the ride-complaint condition types: shimmy; harsh ride; handling; pitch/back slap; stability; bounce/hop; and vibration. “There are two things I deal with at Meritor — shimmy and vibration,” he said. “Why? Because trucks are becoming more user-friendly. They want to be able to live in there and not feel anything on their butt — no shaking or rattling like trucks out there 40 to 50 years ago.

There are Mercedes-Benz type vehicles, these Freightliners and Volvos. Shimmy most of time has to do with front steer tires.” He said the Kent-Moore Electronic Vibration Analyzer (EVA) 2 is a low-cost electronic diagnostic tool to help diagnose low-frequency vibrations. “It's a very high-tech, awesome product,” he said. “If you have shake, rattle, or roll that's vibratory from a rotating mass, it does not find loose suspension items — rotational items only.” Trailer ride height Tony Kockritz, Hendrickson International's regional service manager, said it's important to check trailer ride height, truck ride height, shock absorbers, and bushings. “As regional service manager, I cover eight states and two Canadian provinces, and am in charge of training,” he said. “When I go to fleets, dealers, and repair shops, it's amazing what they don't know. That's something to know on any suspension. “The ride height is the distance between the center line of the axle and the bottom of the sub-frame. If it's a slider box, it's the bottom of the box. If it's a regular trailer flatbed, it's going to be the bottom frame frail.

The easiest way to measure is from that suspension-mounting surface to the top of the axle. And then once you figure out the diameter of the axle, just add the difference. If you have a five-inch diameter axle, take the tape measure and measure from the bottom of the sub-frame of the trailer and to the top of the axle. Take that dimension and add 2½ inches and get the trailer ride height. On all suspensions, there's a description tag that will tell you the ride height of that suspension. “It's important that the ride height is set correctly because you want a maximum amount of jounce, which is up travel, and rebound, which is down travel in the suspension. If the ride height isn't set correctly, what can go wrong? We could have air-spring damage. Shock absorbers can get overextended. Trailer damage is the biggest one — the sub-frame.” He said truck ride height is the same as for trailers, except that “entering from the bottom of the frame rail of the tractor and center line of the axle housing, right where the well is on the axle housing, is where you're measuring it to. On some tractors out there, they may have dual height valves.

If they do, you have to do each side separately. The industry spec is plus or minus 1/8" of what the ride height is.” The official New Zealand road code for heavy vehicles - Information for heavy vehicle drivers Information for heavy vehicle drivers Information for heavy vehicle drivers Heavy combination motor vehicle types Full trailers Full trailer Axles A full trailer has two axle sets, one of which is connected to the towing vehicle by a drawbar that steers the front axle set. Note: the axle set requirements described here apply to heavy trailers. They don't apply to light trailers (that is, trailers with a gross vehicle mass (GVM) of up to 3.5 tonnes). A heavy full trailer must have a front axle set consisting of either: a single axle set, or a tandem axle set. A heavy full trailer must have a rear axle set consisting of either: a single axle set, or a tandem axle set, or a tri-axle set, which is only permitted if the front axle set is a tandem axle set. Overall length The maximum overall length for a full trailer (including drawbar and load) is 11.5 metres.

For a rigid vehicle and full trailer combination (including load, but excluding collapsible mirrors), the maximum overall length is 20 metres. Forward distance For a full trailer, forward distance means the distance from the rear axis to the front of the trailer (excluding the drawbar and front axle set) or its load, whichever is foremost. The maximum distance is 8.5 metres. Rear overhang Rear overhang means the distance from the rear axis to the rear of the vehicle or its load, whichever is greater. The maximum for a heavy full trailer is 4 metres or 50 percent of the wheelbase, whichever is less. The maximum overhang for a light trailer is 4 metres. Wheelbase The wheelbase of a full trailer is the distance from the rear axis of the trailer to the centre of the front axle set of the trailer. Front overhang For full trailers, front overhang means the distance from the centre of the turntable that connects the front axle set to the chassis of the trailer, to the foremost point of the vehicle (including its load, but excluding the drawbar). The maximum is 2.04 metres radius arc ahead of the turntable centre.

Tow coupling For a rigid vehicle towing a heavy full trailer, the tow coupling position must not be further behind the rear axis of the towing vehicle than a distance equal to 45 percent of the wheelbase of the rigid vehicle. Inter-vehicle spacing For full trailers, inter-vehicle spacing means the distance between the towing vehicle (excluding the tow coupling shroud) and the trailer (excluding the drawbar but including the load). The maximum distance is 4 metres. Full trailers also have a minimum inter-vehicle spacing of either 1 metre or half the width of the foremost point of the trailer (including the load but excluding the drawbar), whichever is greater. Width This is the same as for heavy rigid vehicles (see page 206).

Drawbars A drawbar on a full trailer can only have one operating position and cannot be extendable, unless it complies with one of the following: it may only be retractable to facilitate loading or unloading of livestock or goods, provided that the drawbar has only one set of holes for locking pins and these holes are positioned so that the drawbar is fully extended when locked, or if the trailer is used to transport logs, the drawbar may have up to three fixed positions and one sliding position, provided that the drawbar has: one sliding position for long logs, and one or two fixed positions for short logs, and a fixed position for storage of the drawbar when it is out of use while the trailer is being transported on a rigid vehicle or another vehicle. Note: when fully extended, the drawbar dimension must be such that the length of the trailer does not exceed 11.5 metres and the total length of the combination vehicle does not exceed 20 metres. Drawbeam A drawbeam must not be sliding or adjustable.

Gross mass The maximum gross mass of a rigid vehicle and one full trailer in combination is 39 tonnes, unless the towing vehicle has: a twin-steer axle set or a wheelbase of at least 4.25 metres, and at least two motor-driven axles in the rear set of the truck. In addition to these two conditions, the maximum gross mass of the heavy full trailer vehicle must not exceed 42 tonnes, unless: the towing vehicle has a twin-steer axle set or a tri-axle set, or the trailer has two tandem axle sets or the trailer has five axles. Semi-trailers A semitrailer with a quad axle set and two steering axles is limited to 18 metres. Axles A semi-trailer has one axle set, attached to the towing vehicle at one of these two coupling positions: at or forward of the rearmost axle of the towing vehicle (for rigid vehicles with one axle in their rear axle set or where another trailer is the towing vehicle), or not more than 300 millimetres behind the rear axis of the towing vehicle (for rigid vehicles with two or more axles in their rear set).

Note: trailers attached to the towing vehicle behind the above positions are considered simple trailers (including Stinger Steer Vehicles). For more information about simple trailers see Simple trailer . A heavy semi-trailer must have a rear axle set consisting of either: a single axle set, or a tandem axle set, or a tri-axle set, or a quad-axle set, provided the rearmost axle and the first or third axle in this set are steering axles and the semi-trailer does not form part of an A-train or B-train combination. Gross mass The gross mass of a semi-trailer (including its load) is the mass transferred to the ground through the axle(s) of that trailer. Any transferred weight from a following attached trailer is to be included in the calculation of gross mass of the first trailer. The maximum gross mass of a rigid vehicle and one semi-trailer is 39 tonnes, unless it has at least two motor-driven axles in the rear set of the rigid vehicle. Overall Length The maximum overall length for a rigid vehicle and semi-trailer combination (including load, but excluding collapsible mirrors) is 19 metres.

Forward distance For a semi-trailer, forward distance means the distance from the rear axis to the centre of the kingpin. The maximum is 9.2 metres. Rear overhang The maximum rear overhang for a heavy semi-trailer is 4 metres or 50 percent of the forward distance, whichever is less. The maximum for a light semi-trailer is 4.3 metres. Front overhang For semi-trailers, front overhang means the distance from the centre of the kingpin to the foremost point of the vehicle (including its load). The maximum is 2.04 metres radius arc ahead of the kingpin.

Towing two trailers (A-trains and B-trains) A heavy rigid vehicle towing two trailers must be: an A-train (a rigid vehicle connected to a semi-trailer that tows a full trailer), or A-train a B-train (a rigid vehicle attached to two semi-trailers connected at two points of articulation, where the forward distance of the longer trailer divided by the forward distance of the shorter trailer does not exceed 1.4), or B-train a heavy rigid vehicle followed by any combination of two trailers (not an A-train or a B-train), provided the trailer at the rear of the combination has a gross vehicle mass (GVM) that isn't over 3.5 tonnes and the gross mass of the combination is less than 20 tonnes. Note: a light rigid vehicle (for example, a car or ute with a GVM of up to 3.5 tonnes) may only tow one trailer. Light tractors, however, are allowed to tow two trailers at a speed not greater than 50km/h. Axles For an A-train, the rigid vehicle must have at least two motor-driven axles in its rear axle set.

A-trains and B-trains must not have retractable or rear-steering axles. Tow coupling For a B-train, the rearmost semi-trailer must not be coupled further rearward than the rearmost axle of the lead semi-trailer. The coupling point distance for an A-train is the distance between the rear axis of the semi-trailer and the centre of the tow coupling connecting the full trailer to the semi-trailer. The maximum allowed is 30 percent of the forward distance of the semi-trailer. Overall length The maximum overall length for a heavy rigid vehicle towing two trailers (including load, but excluding collapsible mirrors) is 20 metres. Simple trailers Simple-trailer A simple trailer is a trailer that has one axle set, and is not a semi-trailer. A simple trailer is attached to the towing vehicle at a position well behind the position specified for a semi-trailer. Stinger Steer Transporters are simple trailer combination vehicles. Gross mass The gross mass of a simple trailer (including its load) is the mass transferred to the ground through the axle(s) of that trailer. Any transferred weight from the following trailer is to be included in the calculation of the gross mass of the first trailer.

The gross mass of a combined rigid vehicle must not exceed 32 tonnes. Axles A heavy simple trailer must have an axle set consisting of: a single axle set, or a tandem axle set, or a tri-axle set. Overall length The maximum overall length for a simple trailer (including drawbar and load) is 12.5 metres. The maximum overall length for a rigid vehicle and simple trailer combination (including load, but excluding collapsible mirrors) is 22 metres. Forward distance For a simple trailer, forward distance means the distance from the rear axis to the centre of the point of attachment of the towing vehicle. The maximum is 8.5 metres. Rear overhang Rear overhang means the distance from the rear axis to the rear of the vehicle or its load, whichever is greater. The maximum rear overhang for a heavy simple trailer is 4 metres or 50 percent of the forward distance, whichever is less. For a light simple trailer, the maximum rear overhang is 4 metres. Front overhang For simple trailers, front overhang means the distance from the centre of the tow coupling to the foremost point of the vehicle (including its load).

The maximum is 2.04 metres radius arc ahead of the tow coupling. Tow coupling For a rigid vehicle towing a heavy simple trailer, the tow coupling position must be at least 700 millimetres behind the rear axis of the rigid vehicle and not more than a distance equal to 50 percent of the wheelbase of that vehicle. The wheelbase is measured from the rear axis of the rigid vehicle to the foremost axle of that vehicle. Note: for Stinger Steer Transporters, 'tow coupling' includes an articulated fifth wheel attachment with kingpin, or a ball attachment. Inter-vehicle spacing There is no minimum inter-vehicle spacing for simple trailers. The trailer (or its load) may overhang the towing vehicle. Important Drivers of vehicles that tow simple trailers (those with one axle set that aren't semi-trailers) also need to be aware that the simple trailer can impose a large weight on the rear of the towing vehicle that can (by lever action through the chassis of the vehicle) reduce the effective mass bearing on the front axle(s) of the towing vehicle. Simple trailers therefore need to be loaded carefully so that their load is distributed centrally over the axle(s) of the trailer.

This will allow the towing vehicle to maintain front wheel traction. Note: loading on a simple trailer is critical, as there needs to be a small downward force on the tow coupling to make sure a simple trailer remains stable while it's being towed. Pole trailers Pole trailers A pole trailer is a trailer attached to a towing vehicle by a telescoping or sliding pole, which is designed to support a common long load spanning between the trailer and the towing vehicle. Overall length The maximum overall length for a pole trailer is 11.5 metres (drawbar fully extended, but excluding the load). The maximum overall length for a rigid vehicle and pole trailer combination (including load, but excluding collapsible mirrors) is 20 metres. Front overhang Front overhang for pole trailers is the distance from the centre of the turntable on the towing vehicle to the foremost point of the load. The maximum is 2.04 metres radius arc ahead of the turntable centre on the towing vehicle (that is, the load on the trailer may hang forward of the turntable centre on the towing vehicle by this distance).

Gross mass The maximum gross mass of a rigid vehicle and the pole trailer combination is 39 tonnes, unless the towing vehicle has at least two motor-driven axles in its rear axle set. Pole trailers with one axle set A heavy pole trailer with one axle set must have an axle set consisting of: a single axle set, or a tandem axle set, or a tri-axle set. For a pole trailer with one axle set, forward distance means the distance (excluding load) from the rear axis of the trailer to the centre of the point of attachment to the towing vehicle. The maximum distance is 8.5 metres, measured with the drawbar at full extension. Rear overhang is the distance from the rear axis to the rear of the vehicle or its load, whichever is greater. The maximum rear overhang for a heavy pole trailer with one axle set is either 4 metres or 50 percent of the forward distance of that trailer, whichever is lesser. The maximum rear overhang for a light pole trailer with one axle set is 4 metres. Pole trailers with two axle sets A heavy pole trailer with two axle sets must have a front axle set consisting of either: a single axle set, or a tandem axle set.

A heavy pole trailer with two axle sets must have a rear axle set consisting of: a single axle set, or a tandem axle set, or a tri-axle set, which is only permitted if the front axle set is a tandem axle set. For a pole trailer with two axle sets, forward distance means the distance (excluding load) from the front axis of the trailer to the centre of the point of attachment to the towing vehicle. The maximum is 8.5 metres, measured with the drawbar at full extension. For a pole trailer with two axle sets, rear overhang is the distance from the rear axis to the rear of the vehicle or its load, whichever is greater. The maximum for a heavy pole trailer with two axle sets is either 4 metres or 50 percent of the wheelbase of the trailer (where the wheelbase is measured from the rear axis to the centre point of the front axle set), whichever is lesser. The maximum for a light pole trailer with two axle sets is 4 metres.

Question: What is the distance between the axles on a car called
Answer: The wheelbase